8/8/2019 Production activity control cap 11 fall 2007
1/43
Production Activity Controlshop floor control
Concerned with controlling theactual activity of making a product
or delivering a service.
Source: Chapman, Fundamentals of Production Planning and Control
8/8/2019 Production activity control cap 11 fall 2007
2/43
PAC
Planning has already been done and theactual order to produce a product hasbeen executed.
Deals with controlling the priority of the jobs at a work center
Execution control activity.Monitor, prioritize and control.
8/8/2019 Production activity control cap 11 fall 2007
3/43
PAC inputs:
Newly released orders (MRP)Existing order statusRouting information steps, sequence
needed to complete the jobLead time informationStatus of resources (quantity available,
maintenance schedules, machineproblems, etc.)
8/8/2019 Production activity control cap 11 fall 2007
4/43
PAC inputs cont.
Resources number, type, conditions People number, skills, time availability Tools equipment for setup or operation of
the machinery Machine or equipment capacity and downtime Materials needed to complete the order
8/8/2019 Production activity control cap 11 fall 2007
5/43
Information generated by PAC:
Status and location of ordersStatus of critical resources
Performance to standardsScrap / reworkProblems (unscheduled downtime, broken
equipment, etc.)
8/8/2019 Production activity control cap 11 fall 2007
6/43
Need for PAC
Process industries and repetitive assemblylines with a high volume standard product
dont use detailed PAC systems. Onlyneed to monitor the quantity as it isproduced.Industries with smaller quantities of discrete jobs, often use dispatch lists.
8/8/2019 Production activity control cap 11 fall 2007
7/43
Dispatch list = list of jobs to be performed
at a given work center in the order inwhich the jobs should be done.Includes information: Scheduled run date, setup and run time Equipment to be used and specific operation Lot sizes Estimates of capacity available Next work center (where to move the job) Jobs expected to be received at the WC in
some specified time period (future jobs)
8/8/2019 Production activity control cap 11 fall 2007
8/43
The dispatch list is followed by a report tothe PAC system with information on:Part number and quantity producedAny problems (scrap, quality, shortages)
Workforce dataEquipment statusComments, suggestions
8/8/2019 Production activity control cap 11 fall 2007
9/43
PAC and Gantt charts
Gantt chart = simple visual tool used toschedule work according to priority and toassess the status of all jobs ordered.Used to reprioritize jobs if needed.Shows work to be done, expectation of time required, start and end dates, and job
status.Done for each work center or specificmachine.
8/8/2019 Production activity control cap 11 fall 2007
10/43
Prioritizing work
Practice exercise dataSuppose thefollowing jobshave arrivedat a WC in theorder listed:
JOB Due in Hrs. workremaining
A 3 hrs. 4
B 9 hrs. 2
C 4 hrs. 1
D 15 hrs. 5E 11 hrs. 3.5
F 19 hrs. 5
8/8/2019 Production activity control cap 11 fall 2007
11/43
Prioritizing Work methods
1. Due date = Job with earliest due date isdone first. Often used with MRP planning.
8/8/2019 Production activity control cap 11 fall 2007
12/43
Due date
job Due in Workremaining Start time Completiontime Late?
A 3 hrs. 4 hrs. 0 4 Yes
C 4 hrs. 1 hr. 4 5 Yes
B 9 hrs. 2 hrs. 5 7 No
E 11 hrs. 3.5 hrs. 7 10.5 No
D 15 hrs. 5 hrs. 10.5 15.5 Yes
F 19 hrs. 4 hrs. 15.5 19.5 Yes
8/8/2019 Production activity control cap 11 fall 2007
13/43
2. SPT Shortest processing time = quick jobs are done first.
A lot of jobs are completed quickly.Leaves long jobs for last and sometimesmakes them late. (customer service andbig orders)
8/8/2019 Production activity control cap 11 fall 2007
14/43
Shortest processing time
Job Due in Workremaining
Start time Completiontime
Late?
C 4 hrs. 1 hr. 0 1 No
B 9 hrs 2 hrs. 1 3 No
E 11 hrs 3.5 hrs. 3 6.5 No
A 3 hrs. 4 hrs.* 6.5 10.5 Yes
F 19 hrs. 4 hrs.* 10.5 14.5 No
D 15 hrs. 5 hrs. 14.5 19.5 yes
8/8/2019 Production activity control cap 11 fall 2007
15/43
3. Total slack:
Total time until the job is due-Total processing time____
Total slack
Slack = buffer time, time that can passwithout danger of the job being late.
Work first the jobs with the least total slack(greatest danger of being late)
8/8/2019 Production activity control cap 11 fall 2007
16/43
Total slack
Job Due in Workremaining Slack Start time Completiontime
A 3 hrs. 4 hrs. -1 hr. 0 4
C 4 hrs. 1 hr. 3 hrs. 4 5
E 11 hrs. 3.5 hrs. 6.5 hrs. 5 8.5
B 9 hrs. 2 hrs. 7 hrs. 8.5 10.5
D 15 hrs. 5 hrs. 10 hrs. 10.5 15.5
F 19 hrs. 4 hrs. 15 hrs. 15.5 19.5
8/8/2019 Production activity control cap 11 fall 2007
17/43
4. Slack per operation:
Total slack / number of operations left
Work first the job with the least slack per
operation
Gives average slack at each operation
instead of total slack for the entire job.
8/8/2019 Production activity control cap 11 fall 2007
18/43
Job Due in Slack # operations Slack per operation
Workremaining
A 3 hrs. -1 3 -.33 4 hrs.
B 9 hrs. 7 9 .77 2 hrs.
C 4 hrs. 3 4 .75 1 hrs.
D 15 hrs. 10 15 .66 5 hrs.
E 11 hrs. 6.5 11 .59 3.5 hrs.
F 19 hrs. 15 19 .79 4 hrs.
8/8/2019 Production activity control cap 11 fall 2007
19/43
Job Due in Slack per operation
Workremaining
Start Completion Late?
A 3 hrs. -.33 4 hrs. 0 4
E 11 hrs. .59 3.5 hrs. 4 7.5
D 15 hrs. .66 5 hrs. 7.5 12.5
C 4 hrs. .75 1 hrs. 12.5 13.5
B 9 hrs. .77 2 hrs. 13.5 15.5
F 19 hrs. .79 4 hrs. 15.5 19.5
8/8/2019 Production activity control cap 11 fall 2007
20/43
5. First come, first served Assumes that the first job is also neededfirst (doctors office)
Perceived as fair.Really?
8/8/2019 Production activity control cap 11 fall 2007
21/43
6. Critical ratio:
Time remaining until due / work remaining
Work remaining = total processing time If critical ratio is greater than 1 : there is slack If critical ratio = 1 : there is no slack If critical ratio is less than 1 : past due, late
rule: work first job with lowest critical ratio Considered best rule
8/8/2019 Production activity control cap 11 fall 2007
22/43
Critical ratio
Job Due in Workremaining
Ratio Start time Completiontime
Late?
A 3 hrs. 4 hrs. .75 0 4 Yes
D 15 hrs. 5 hrs. 3 4 9 No
E 11 hrs. 3.5 hrs. 3.14 9 12.5 Yes
C 4 hrs. 1 hr. 4 12.5 13.5 Yes
B 9 hrs. 2 hrs. 4.5 13.5 15.5 Yes
F 19 hrs. 4 hrs. 4.75 15.5 19.5 Yes
8/8/2019 Production activity control cap 11 fall 2007
23/43
These scheduling rules apply in productionenvironments where integrated productioncontrol systems are not used (smaller jobshop environments).
Integrated approaches (MRP) provide their own scheduling priorities.
8/8/2019 Production activity control cap 11 fall 2007
24/43
Scheduling: estimation of when a job will reach awork center and when the job will be completed.
Two approaches:1. backward scheduling : start with the due
date (promised date) and use lead timeto estimate when job will reach eachcenter. (MRP)
2. Forward scheduling: start when the job
will be released into the productionprocess. Estimate final completion dateand this becomes the promise date.
8/8/2019 Production activity control cap 11 fall 2007
25/43
Example data
It is now the start of day 214, and there is
one shift in the operation with 7 productivehours. The job calls for a quantity of 100to be built:
8/8/2019 Production activity control cap 11 fall 2007
26/43
Day 214; 7 work hours; 100 units
Operation Total lead time for 100 u.
A 21 Hours
B 14 hoursC 35 hours
D 7 hours
E 10.5 hours
F 3.5 hours
8/8/2019 Production activity control cap 11 fall 2007
27/43
Forward scheduling
Operation Lead timehours
Completed
A 21 End of day 216 (3 shifts:214,215,216)
B 14 End of day 218
C 35 End of day 223
D 7 End of day 224
E 10.5 Half through day 226
F 3.5 End of day 226
8/8/2019 Production activity control cap 11 fall 2007
28/43
This implies that we can deliver theproduct on day 227.
Lead time includes setup, run, queue and
move time.
queue time = time a job must wait to be
processed once it has been moved to theoperation. Largest and most variable of allthe elements of lead time.
8/8/2019 Production activity control cap 11 fall 2007
29/43
Backward scheduling
Suppose thesalespersonhas promisedthe job for
delivery on day240 using astandard quotedlead time.
Job must befinished onday 239.
Operation;Lead time
Must becompletedby:
Must startby:
F; 3.5 hrs. End of 239 Mid-day 239
E; 10.5 hrs. Mid-day 239 Start of 238
D; 7 hrs. End of 237 Start of 237
C; 35 hrs. End of 236 Start of 232
B; 14 hrs. End of 231 Start of 230
A; 21 hrs. End of 229 Start of 227
8/8/2019 Production activity control cap 11 fall 2007
30/43
LoadingWork center load: total time estimate to complete
all the jobs at a given work center. Measured intime units (hours). Two approaches:
1. Infinite loading : jobs are loaded according towhen the customer needs them, regardless of capacity.
Assume the work center has infinite capacity.Need for capacity expanding alternatives(overtime, temporary workers).
8/8/2019 Production activity control cap 11 fall 2007
31/43
Loading2 .
Finite loading : known measurable finite capacityfor the work center.Work is moved to the next time period if there is no
more capacity in the given period.
Advantages:Smoothing the loadSave on extra expenses
Stability of the work center Disadvantages:
Customer service
8/8/2019 Production activity control cap 11 fall 2007
32/43
Methods for loading a work center
1. V ertical loading : jobs are loaded into thecenter job by job according to a priorityrule (due date, critical ratio, etc.).Focus is the work center, with the jobloaded work center by work center, one
job at a time.
8/8/2019 Production activity control cap 11 fall 2007
33/43
Methods for loading a work center
2. H orizontal loading: the highest priority jobis loaded work center by work center intoall the work centers required. Then do thesame for the next jobs.
Used in the finite scheduling system.
Focus is on the job.
8/8/2019 Production activity control cap 11 fall 2007
34/43
Loading example:
A work center (X) has the following jobs,which are listed in the order in which theyarrived at the work center.
The work center uses due date with firstcome, first serve to break any ties.
The current day is the start of day 137, andthere are 7 productive hours in a day
(420 minutes).
8/8/2019 Production activity control cap 11 fall 2007
35/43
Job(arrival
order)
Quantity Due day Setup time(min.)
Standard per piece (min.)
A 130 136 10 1.5
B 100 137 30 1.8
C 50 137 10 0.6
D 200 138 25 0.8
E 120 138 15 1.1
F 100 138 20 1.3
8/8/2019 Production activity control cap 11 fall 2007
36/43
V ertical loading and infinitecapacity
Need to first determine the time it shouldtake to complete each job at standard.
See next table
8/8/2019 Production activity control cap 11 fall 2007
37/43
Job; Q Time std. X Q Setup time Total time
A; 130 130x1.5=195 min. 10 min. 205 min.
B; 100 100X1.8=180 min. 30 min. 210 min.
C; 50 50X0.6=30 min. 10 min. 40 min.
D; 200 200X.08=160 min. 25 min. 185 min.
E; 120 120X1.1=132 min. 15 min. 147 min.
F; 100 100X1.3=130 min. 20 min. 150 min.
8/8/2019 Production activity control cap 11 fall 2007
38/43
Infinite loadingLoad the work center according to duedate. Jobs A, B, and C would be loadedinto day 137.
Jobs D, E, and F would be loaded into day138.It will require 455 minutes in day 137 and482 minutes in day 138.
Minutes available =420Need for overtime
8/8/2019 Production activity control cap 11 fall 2007
39/43
Finite loading : 420 minutes available
Only try to complete jobs A and B in day 137.Total minutes required= 415.5 minutes left. Try to start setup for job C.Day 138: finish job C and then complete jobs Dand E.53 minutes left; do setup and start running job F.Complete approximately 25 of the 100 items (53min.- 20 min. setup =33 min.33 min./1.3 min. per item = 25.4 itemsJobs C and F will be late
8/8/2019 Production activity control cap 11 fall 2007
40/43
Infinite vs. Finite
Infinite loading assumes flexibility incapacity and gives priority to due dates,regardless of the increase in costs.Finite loading assumes no flexibility incapacity and costs. Problems withcustomer service levels.
8/8/2019 Production activity control cap 11 fall 2007
41/43
It has been assumed that lead time isknown, constant, and accurate. This is not
always true. We might have different actualLT.
Corrective actions: (different Std. and realtimes) Subcontracting or purchasing components
Lot splitting = work only on minimal amountreally needed. Leave the rest for a later date.
8/8/2019 Production activity control cap 11 fall 2007
42/43
Corrective actions cont.
Operation overlapping = moving part of theorder to the subsequent operation before theentire order is ready for that next operation.
Operation splitting = assigning moreresources to the order so that processing canproceed more quickly.
8/8/2019 Production activity control cap 11 fall 2007
43/43
Corrective actions cont.
Alternative routings = moving the job tooperations not normally used for itsproduction. Used when primary production
resources are not available.
Order cancellations = costs to complete arehigher than expected profit from the order.